1. Field on the Invention
The invention relates to the field of turbine engines and gas turbine engines in particular and concerns the assembly of an element forming a support for a labyrinth seal on a rotor of the engine.
2. Description of Related Art P A gas turbine engine comprises at least one rotating shaft mounted inside a fixed structure forming the stator, and in which it is supported by bearings. The bearings are enclosed in housings receiving, in particular, lubricating oil. Seals, generally labyrinth seals, are positioned between the support for a bearing and the rotor, so as to prevent oil which serves to lubricate the bearing from escaping out of the bearing zone and contaminating the engine.
A labyrinth seal comprises a moveable part integral with the rotor and a fixed part integral with the stator. The moveable part consists of a revolving part at the surface of which a plurality of radial blades or seal teeth are provided perpendicular to the axis of rotation. The part is bolted onto the rotor close to the bearing of which it must now provide a seal. The blades of this part are held at a small radial distance from a ring integral with the fixed part, so that any flow of fluid from the zone under excess pressure on one side of the blades to the lower pressure zone on the other side of the blades is reduced as much as possible. The ring is made of a material that wears or deforms preferentially compared with the blades so that the seal can absorb radial expansions during the different operating phases of the engine. It consists of a honeycomb or of an abradable type of material.
The arrangement and assembly of such a seal has been shown in FIGS. 1, 2 and 3, in the region of the turbine bearing of an aeronautical gas turbine engine. FIG. 1 shows the part of the engine having the bearing 1 of the low pressure rotor. The bearing support 3 is located in the oil recovery housing 5 on the stator side. The rotating part 7 supporting the labyrinth seals and partly delimiting the bearing chamber here has a U-shaped section with a central radial part. It is mounted on a radial flange 91 of the shaft 9 of the motor on which the drive component or cone 93 is fixed connecting the turbine module 10, here the low pressure turbine, to the shaft 9. The moveable seal support is provided with several groups of radial blades 71, each cooperating with a ring 31 and 51, integral with the bearing support 3 and the oil recovery housing 5 respectively.
FIGS. 2 and 3 show in greater detail the assembly of the seal support 7 on the turbine rotor. The seal support is fixed to the shaft by axial bolts 95 passing through the wall of the drive cone 93 and the flange 91 of the shaft, while holding them assembled. These bolts are distributed, by reason of the load transmitted by the turbine to the shaft, on the periphery of the flange 91. Extraction holes 91A are also provided. There are four of these that are positioned along two diameters at a right angle. The extraction holes machined in the flange 91 are axial, and flared out on the side of the drive cone 93. The extraction holes 91A communicate with the holes 75 machined in the radial portion 73 of the seal support 7. It will be noted that, contrary to the housings for the bolts 95, they do not extend into the wall of the cone 93. A cylindrical insert 91B is housed in each of the four holes 91A. The inserts comprise a collar 91B1 extending into the flared-out part of the holes 91A and ensure that they are axially immobilized. These holes, which remain free from a bolt during the time when the motor is operational, have the function of making it easier to dismantle the drive cone. With this aim in mind, screws are introduced into each of the holes 91A at the time that the engine is dismantled. By screwing the extraction screws into the inserts 91B housed in the holes 91A, their stems are applied against the wall of the cone which is blind at this point and in this way an axial force is created tending to separate the cone 93 from the rotor 9.
Cracks are liable to form in the revolving part 7. Indeed, tightening conditions induce a risk of starting a crack by fretting, at the edges of a free extraction hole.